1. Field of the Invention
The present invention relates to two-dimensional symbologies, and, in particular, to a method and apparatus for characterizing the quality of two-dimensional symbols in pixel images.
2. Statement of Related Art
U.S. Pat. Nos. 4,874,936 (Chandler et al.) and 4,896,029 (Chandler et al.) disclose articles, processes, and systems for polygonal information encoding, whereby information is encoded in a two-dimensional symbol comprising a plurality of polygons and an acquisition target.
The '936 and '029 patents disclose a two-dimensional symbol that comprises an acquisition target with a bull's-eye pattern that conveys information for finding the symbol, and an array of differently shaded hexagons in which alpha-numeric type data is encoded. Such a symbol may be printed using a printer having a resolution of about 80 to 100 pixels per inch. At this resolution, each hexagonal element of the symbol only approximates a true hexagon, as shown in FIGS. 13, 14, and 15 of the '029 patent. Printers with greater or lower resolution are able to print symbols having elements that more or less closely approximate true hexagons. The further the approximation from a true hexagon, the more errors that may occur during the process of decoding the information stored in the symbols. Thus, the printer resolution used directly affects the ability of a symbol reader to decode a symbol.
In addition, symbols may get distorted in the printing processes. Distortion in the image of a printed symbol may also be caused by the optical sensor system used to generate the image of the printed symbol. Such distortions may also lead to errors in the decoding of the printed symbol.